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    <meta charset="UTF-8">
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    <title>Document</title>
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<body>
    <script>
        //原型对象的应用 扩展内置对象方法
        console.log(Array.prototype);
        Array.prototype.sum=function(){
            var sum=0;
            for(var i=0;i<this.length;i++)
            {
                sum+=this[i];
            }
            return sum;
        }
        var arr = [1,2,3];
        console.log(arr.sum());
        console.log(Array.prototype);
        var arr1 = new Array(11,22,33);
        console.log(arr1.sum());
    </script>
</body>
</html>